PDF Compression: Reducing File Size Without Sacrificing Quality
Large PDF files are difficult to share via email and slow to load on mobile devices. Learn how PDF compression works and how to strike the right balance between file size and visual quality.
Key Takeaways
- PDF file size is determined by several factors: embedded images, fonts, metadata, and the complexity of vector graphics.
- Reducing image resolution from 300 DPI to 150 DPI can cut file size by 75% with minimal visible difference on screens.
- Avoid compressing PDFs that contain technical drawings, architectural plans, or high-resolution photographs intended for print.
Merge PDF
Combine multiple PDF files into one document.
Understanding PDF File Size
PDF file size is determined by several factors: embedded images, fonts, metadata, and the complexity of vector graphics. Images are typically the largest contributor, often accounting for 80-90% of total file size in image-heavy documents.
Compression Techniques
Image Downsampling
Reducing image resolution from 300 DPI to 150 DPI can cut file size by 75% with minimal visible difference on screens. For documents intended only for on-screen viewing, 72-96 DPI is usually sufficient.
Font Subsetting
Instead of embedding an entire font file (which can be 1-5 MB per font), subsetting includes only the characters actually used in the document. This can save significant space in documents that use decorative or CJK fonts.
Removing Metadata
PDFs can contain hidden metadata including edit history, comments, form field data, and embedded thumbnails. Stripping this metadata can reduce file size by 5-20% and also improves privacy.
Quality Presets
| Preset | Target DPI | Best For |
|---|---|---|
| Screen | 72 DPI | Email, web viewing |
| eBook | 150 DPI | Tablets, e-readers |
| 300 DPI | Professional printing | |
| Prepress | 300+ DPI | Commercial printing |
When Not to Compress
Avoid compressing PDFs that contain technical drawings, architectural plans, or high-resolution photographs intended for print. In these cases, the quality loss may be unacceptable.
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